Patent GB-709017-A (GB)
Title: Improvements in or relating to servo-assisted braking mechanism
Inventor: EDGE STANLEY HOWARD
IPC: B60T13/24
Filed: 1951-05-16
Abstract: 709,017. Servo-assisted braking mechanism. CLAYTON DEWANDRE CO., Ltd. May 15, 1952 [May 16, 1951; June 14, 1951], Nos. 11494/51 and 14132/51. Class 103(1) In a servo-assisted mechanism for operating the brakes of a road vehicle, a hydraulic cylinder is adapted to be interposed in a fluid connection between a pedal or like operated master cylinder and the brake-applying cylinders, a vacuum or fluid-pressure operated servo device is disposed at one end of said hydraulic cylinder, and is operable to advance a displacement member or ram into said hydraulic cylinder to cause pressure to be created therein and transmitted to the brake-applying cylinders, a device acting as a non-return valve is disposed around said displacement member or ram and operable to permit passage of liquid both from the master cylinder to the hydraulic cylinder and in the reverse direction when the displacement member or ram is in its inoperative position but to permit passage of liquid in the former direction only when the displacement member or ram is advanced in the hydraulic cylinder, and a. valve mechanism is adapted to be operated by pressure transmitted from the master cylinder for initiating and controlling the operation of the servo device, said valve mechanism being arranged to react upon or balance the effort applied to the pedal or the like by the operator. In the operative position shown in Fig. 2, hydraulic pressure is created in the master cylinder 2 by pressure on the pedal 1 and is transmitted to the annular chamber 4 in the housing 5 and thence through passage 10 to the plunger mechanism 12 which in turn transmits a lifting motion to the valve mechanism 13, 16, 19, 18, 26, similar to that described in Specification 687,658, which controls the vacuum supply from conduit 24 to the vacuum servo device 9 and urges the piston rod or ram 6 into the hydraulic cylinder 30, thereby causing hydraulic pressure to be transmitted through conduit 31 to the brake applying cylinders. Surrounding the piston ram 6 is an annular resilient seal 34 which acts as a non-return valve permitting hydraulic fluid to pass through from the master cylinder 2 to the brake applying cylinders, in the operative position, but not in the reverse direction. Hydraulic fluid is allowed to discharge from the hydraulic cylinder 30 into the master cylinder 2 when the ram 6 is in the fully retracted or inoperative position by reason of the recess 38 in the end of the ram 6, the small radial ports 39, the annular recess 40 in the seal 34 and the ports 33 into the annular recess 4. A similar type of resilient seal 43, provided, as in the case of seal 34, with an annular recess whereby the spragging action of the seal is reduced, is fitted around the plunger 12. Fig. 3 shows an alternative arrangement of the valve operating mechanism so that the valve-actuating lever 13 is disposed within the servo cylinder 9; the mechanism in this case being shown in its inoperative position. Reference has been directed by the Comptroller to Specification 694,582.